The present invention relates generally to methods and systems for inducing fractures in a subterranean formation and more particularly to methods and systems that utilize explosive and cryogenic means to establish fluid communication to areas away from the well bore walls.
Oil and gas wells often produce hydrocarbons from subterranean formations. Occasionally, it is desired to add additional fractures to an already-fractured subterranean formation. For example, additional fracturing may be desired for a previously producing well that has been damaged due to factors such as fine migration. Although the existing fracture may still exist, it is no longer effective, or is less effective. In such a situation, stress caused by the first fracture continues to exist, but it would not significantly contribute to production. In another example, multiple fractures may be desired to increase reservoir production. This scenario may be also used to improve sweep efficiency for enhanced recovery wells such as water flooding steam injection, etc. In yet another example, additional fractures may be created to inject with drill cuttings.
Conventional methods for initiating additional fractures typically induce the additional fractures with near-identical angular orientation to previous fractures. While such methods increase the number of locations for drainage into the well bore, they may not introduce new directions for hydrocarbons to flow into the well bore. Such conventional methods are generally used for placing additional fractures at the approximate same location after a very long production of the fracture or used for placing additional fractures in the well at that same time frame but far away from the location of the previous fracture (such as in a different zone in the well). Conventional methods may also not account for or, even more so, utilize stress alterations around existing fractures when inducing new fractures. Moreover, placing additional fractures that are located at the same location as the first will simply reopen the first fracture. Hence, conventional methods are usually applicable for refracturing after a long term well production (after it is depleted) or for fracturing in a completely different zone.
An improved method and system for inducing a first fracture having a first orientation and a second fracture having a second orientation is disclosed in U.S. application Ser. No. 11/545,749 (“'749 application”) which is incorporated herein by reference in its entirety. In accordance with the invention disclosed in the '749 application, Pin-Point stimulation technologies such as hydrajetting operations are used to establish the first fracture, and after a short time delay, the Pin Point stimulation technology is used to establish fluid communication to areas which have been modified by a first fracture. Specifically, a first fracture is used to modify the local stresses to allow the subsequent second fracture in a direction different from the first fracture. In this manner, the second fracture will reach more productive regions in the formation. The Pin-Point stimulation technology was particularly selected because, as the first fracture starts to close, the stresses near the well bore quickly return to their original condition. This is caused by the fact that the fracture mouth is “dangling” or unsupported; thus stresses normalize quickly. Mere pressurization of the well bore such as by using conventional methods would just re-open this first fracture. Using the Pin-Point stimulation technology, a pressure point is created away from the well bore by reperforating using Bernoulli pressurization, thus reaching locations with modified stresses and hence capable of initiating the second fracture into a completely different direction.
One suitable hydrajetting method, introduced by Halliburton Energy Services, Inc., is known as the SURGIFRAC and is described in U.S. Pat. No. 5,765,642. The SURGIFRAC process may be particularly well suited for use along highly deviated portions of a well bore, where casing the well bore may be difficult and/or expensive. The SURGIFRAC hydrajetting technique makes possible the generation of one or more independent, single plane hydraulic fractures. Furthermore, even when highly deviated or horizontal wells are cased, hydrajetting the perforations and fractures in such wells generally results in a more effective fracturing method than using traditional perforation and fracturing techniques.
Another suitable hydrajetting method, introduced by Halliburton Energy Services, Inc., is known as the COBRAMAX-H and is described in U.S. Pat. No. 7,225,869. The COBRAMAX-H process may be particularly well suited for use along highly deviated portions of a well bore. The COBRAMAX-H technique makes possible the generation of one or more independent hydraulic fractures without the necessity of zone isolation, can be used to perforate and fracture in a single down hole trip, and may eliminate the need to set mechanical plugs through the use of a proppant slug.
However, Pin-Point stimulation techniques such as SURGIFRAC and COBRAMAX-H may not be appropriate in certain circumstances. For instance, the wait period for the requisite tools may be too long. As a result, the well operations may be delayed in order for the necessary tools to be prepared and delivered to the field.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.